I have a patient who needs #4 implant placed. My concern is that this is too close to the sinus. The implant I have planned is 3.75x8mm. Do you think its too close?

It is safe to place an implant right into the floor of the sinus. A good rule of thumb is for it not to stick into the sinus more than 2mm or else it can cause infections, nosebleeds, or other sinus problems. For this case it looks like you will be only 1mm into the sinus—which I wouldn’t be concerned about for a healthy patient with no pre-existing sinus issues.

Be careful when you drill, try not to rupture the membrane with your drills. The implant should gently be inserted and will just engage the floor of the sinus—if it goes just a smidge beyond that it can gently push the membrane up a little. But from the looks of it, it should not be sticking into the sinus more than 1mm.

If you stick it in more than 2mm, what happens is that it can protrude past the floor and past the sinus membrane— and it will accumulate bacteria, which can lead to infections.